MPO and colitis: On the other hand, quercetin reduces neutrophil and macrophage infiltration in the colon tissue of DSS-induced colitis in C57BL/6 mice [14] and inhibits production of colon damaging cytokines via suppressing the activity of myeloperoxidase (MPO), heme oxygenase-1 (Hmox1, HO-1), and inducible nitric oxide synthase (iNOS) [28, 34].